The present invention relates to a high frequency communication device, and more particularly to a high frequency communication device having a box in which a high frequency circuit element for processing signals in a frequency band of microwaves or millimeter waves is mounted.
In an automobile radar device using millimeter wave signals or in a high frequency wireless communication device or wireless terminal device using radio wave signals in a frequency band of 300 MHz or higher, a box thereof is so structured as to contain a single multi-function semiconductor element or integrated circuit (IC), a package comprising a plurality of ICs, or a high frequency circuit element comprising a plurality of mutually connected ICs including circuits for filtering and other functions for the purpose of realizing reduction in size and cost and incorporating multiple circuit functions.
As an example of a communication device having such a structure as mentioned above, there is an automobile radar transmitter-receiver reported in the Proceedings of the 1997 Institute IEICE Conference C-2-121 xe2x80x9c60 GHz Band Millimeter Radar Unitxe2x80x9d. This device is structured to contain a millimeter wave (60 GHz band) transmitter-receiver circuit in a box thereof having plane internal surfaces. As another example, there is an RF subsystem found at the lower part of the front page photograph of the Catalog xe2x80x9cRF, Microwave and Millimeter Wave, Single and Multi-Function Components and Subassembliesxe2x80x9d of M/A-COM Co. U.S.A., issued in 1996. This RF subsystem is so designed that a plurality of high frequency (RF) function circuit elements are contained in a box thereof, which is partitioned into a plurality of areas by internal metallic walls for reducing possible electromagnetic interference among the function circuit elements.
Further, as another example, there is a transmitter-receiver reported in the Proceedings of the APMC98 Conference TU1A-3 xe2x80x9cAn Integrated Millimeter Wave MMIC Transceiver for 38 GHz Bandxe2x80x9d (in 1998). In this transmitter-receiver, a box thereof contains a plurality of transmitting-receiving MMICs and a dielectric substrate having passive circuits for connecting the MMICs, and the cover of the box is arranged to provide grooves for signal propagation.
Still further, as another example, there is a communication device reported in the Proceedings of the APMC98 Conference TU1A-1 xe2x80x9cA Cost-Effective RF-Module for Millimeter-Wave Systemsxe2x80x9d (in 1998). This communication device is so structured that a box thereof contains a communication MMIC, a circuit substrate having passive circuits for connecting the MMIC, and a planar antenna.
Where a plurality of function elements are contained in a single box structure, physical distances among the function elements are shortened as the number of function elements is increased under condition that the size of the box is constant. Alternatively, with an increase in the number of function elements, it is required to increase the size of the box with respect to half of a free-space wavelength of a signal frequency (e.g., approximately 1.95 mm at 77 GHz). In either case, electromagnetic energy of a signal frequency emitted from a point of any function element or IC into the inside of the box readily propagates to another function element contained in the box through space therein, causing a variety of malfunctions due to electromagnetic coupling. For instance, in a transmitter-receiver or a millimeter-wave automobile radar transmitter-receiver module, if a part of a signal emitted from a transmitting function element into the inside of a box thereof propagates to a receiving function element contained in the box, there occurs such a trouble as saturation of a receiver circuit or increased noise in the receiver circuit. In particular, where the size of a box is considerably large with respect to half of a free-space wavelength of a signal frequency, a multiplicity of resonance frequencies signal components may be present in the inside of the box to worsen a condition of such a trouble as mentioned above.
Similarly to these phenomena, undesired energy emitted into the inside of a box readily causes undesired emission out of the box which unintentionally serves as a kind of antenna. On the contrary, external electromagnetic energy is likely to be received through the box, giving rise to a serious problem in requirements concerning EMI (Electro-Magnetic Interference) and EMC (Electro-Magnetic Compatibility).
To alleviate these problems, particularly electromagnetic interference in the inside of a box, a conventional communication device using such prior art as aforementioned has a box structure which is divided into a plurality of small areas by metallic partitions or a metallic box structure which provides local cut-off waveguides along signal paths for protection against undesired emission. In implementation of these conventional techniques, it is required to form a complex metallic box structure or to divide a high frequency passive circuit substrate into a plurality of sections. Further, due to formation of the complex metallic box structure or division of the passive circuit substrate, there occurs difficulty in mounting arrangement of semiconductor ICs and passive circuit parts, resulting in hindrance to mass-production of communication devices and reduction in manufacturing cost thereof.
It is therefore an object of the present invention to provide a high frequency communication device which can reduce electromagnetic interference inside and outside a box thereof, i.e., undesired electromagnetic coupling among internal circuit elements in the box and undesired interference with the internal circuit elements by an external electromagnetic wave, without giving hindrance to mass-production and reduction in manufacturing cost.
In accomplishing this object of the present invention and according to one aspect thereof, there is provided a high frequency communication device having an antenna and a box containing at least a high frequency circuit element which operates with a high frequency signal in a microwave or millimeter wave frequency band, wherein at least a part of a wall constituting the box has at least one periodic structure which provide a periodic pattern of materials or mechanical configurations. The periodic structures in the box are formed to serve as a filter which has a non-propagating frequency band corresponding to a frequency band covering an undesired electromagnetic emission inside the box.
The high frequency communication device may be any of a receiver device, a transmitter device, and a transmitter-receiver device. The high frequency circuit element may be any of a passive element, an IC, an LSI, and a package containing them, including lines for connection thereof. The antenna may be disposed at any position in the inside or outside of the box or on a wall surface of the box. xe2x80x9cAt least a part of a wall constituting the boxxe2x80x9d in the above statement signifies at least a part of a side wall of the box, a part of the ceiling part thereof, or a part of a mounting surface of a function element such as a semiconductor IC.
In the high frequency communication device according to the present invention, simple periodic structures are formed on a part of the box thereof to confine undesired electromagnetic emission energy locally in the inside of the box. This arrangement substantially reduces interference due to undesired electromagnetic emission energy to prevent a possible problem in requirements concerning EMI and EMC, and also attenuates undesired emission energy received from an external electromagnetic emission source to suppress interference.
In a situation where a plurality of undesired electromagnetic emission frequencies may be present in the inside of the box, a plurality of interference problems can be solved by providing different kinds of periodic structures at respective parts in the box. Further, in a case where periodic structures are provided on the ceiling part of the box, for example, the ceiling part may be designed as a lid of the box. Thus, the other parts of the box may be arranged in a simple form (e.g., rectangular parallelepiped) which is considerably large with respect to half of a free-space wavelength of a signal frequency. This arrangement allows the use of a single large-sized high frequency circuit substrate for facilitating the mounting of semiconductor ICs in the box, thereby making it possible to realize a module including the box at low cost.
According to the present invention, it is therefore practicable to realize an advanced multi-function high frequency communication system at low cost without sacrificing overall characteristics thereof. Further, since a filter characteristic based on periodic structures may be provided in a design independent of secure metallic contacting in most cases, the present invention makes it possible to reduce variations in mass-production and deterioration with age concerning characteristics of box products for high frequency transceivers such as millimeter wave automobile radar devices.
The above-mentioned and other features and objects of the present invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings.